Voltage limiter



Jan. 24, 1956 o. c. HALL 2,732,494

VOLTAGE LIMITER Filed July s, 1955 fx oo M^f m m O Q ro co rn m VL V MNH-AM- m cu ro N ('Q cu 0+ N (fr, a POI g #VM- i;m N m U) [I INVENTOR (B35VILLE C. HALL United States Patent O VOLTAGE LlMITER Orville C. Hall, Baltimore, Md., assignor, by mesne assignments, to the United States of Americaas represented by the Secretary oli the Navy Applicatign Jury s, 1953, serial No. 366,6ss 4 claims. (ci. 25o- 27) This invention relates to voltage limiters and more particularly to voltage limiters in which the limited voltage is unaffected by changes in the supply voltage.

In systems employing frequency shift keying for Teletype operation, a direct keying signal supplies the deviation information. This signal may vary in amplitude and produce and frequency deviation when none is desired. For this reason some type of voltage limiting means must be used at the input to the frequency shift control apparatus. The usual vacuum tube limiters suffer from changes in gain as functions of both anode supply and filament supply voltages. A change in gain of the limiter results in a variation in the limited level of the output voltage, and affects the frequency shift control apparatus to produce an unwanted frequency deviation. Although stable anode supply voltages are readily attainable through the use of regulated power supplies, the same is not the case for the filament or alternating voltage supplies.

It is an object of this invention to provide a new and improved voltage limiter.

Another object of this invention is to provide an improved voltage limiter in which the limiting level is not affected by variations in lament supply voltages.

Other objects and advantages of the invention will hereinafter become more fully apparent from the following description of the annexed drawings, which illustrate a preferred embodiment, and wherein the single figure of the drawing is a diagram of the circuit of this invention.

Referring in detail to the single figure of the drawing the reference numerals 11 and 12 designate input terminals to which signals to be limited are applied and across which a resistor 13 is connected. A resistor 14 connects the input terminal 11 to a control grid 16 of a vacuum triode 15 which also contains an anode 17 and a cathode 18. The output signal is taken from the anode 17 and is fed through a resistor 19 to a control grid 22 of a second vacuum triode 21 which contains an anode 23 and a cathode 24. A grid resistor 25 connects the control grid 24 to ground. The cathode 18 of the triode 15 is coupled by a resistor 26 to the cathode 24 of the triode 21 and the two cathodes are connected to ground by a cathode resistor 27. A thyratron 28 having an anode 29, a control grid 30 and a cathode 31 has its anode 29 directly connected to the anode 23 of the triode 21. A regulated power supply 32 supplies energy to the anode 17 through an anode load resistor 33 and to the anodes 23 and 29 through a common load resistor 34. A resistor 35 shunts the thyratron 28 and the resistor 34 to maintain a continual bleeder current ow through resistors 36 and 37 which connect the cathode 31 to ground. The control grid 30 is connected to the junction of the resistors 36 and 37 and is biased by the voltage drop across the resistor 36. The limited output is taken from the circuit by the output terminals 38 and 39.

In the absence of a positive signal at the terminals 11 and 12, triode 21 conducts, drawing a current through the common anode load resistor 34. The voltage drop across ICC the resistor 34 is sufficient to lower the voltage at the anode 29 of the thyratron 28 below the value necessary for the thyratron 28 to fue. When the thyratron 28 does not conduct, the only current passing through the cathode resistors 36 and 37 is the bleeder current which is carried by the resistor 35. The voltage output at the output terminals 38 and 39 is low. When a positive signal appears at the input terminals 11 and 12, the conduction through the triode increases, increasing the bias applied to the triode21 by the cathode resistor 27 Y and cutting-ofi the triode 21. The voltage at the anode 29 of the thyratron 28 then rises and the thyratron 28 lires. Current ow through the resistors 36 and 37 increases and the output voltage at the terminals 38 and 39 increases to a second higher value.

Since the power supply 32 is regulated, current flow through the resistors 36 and 37 in each condition of the thyratron 28 is constant. Since the thyratron 28 is a cold cathode tube, there is no filament voltage to introduce distortion into the output signal.

The described device produces two regulated output voltages for two conditions of input signals. Since a regulated power supply is utilized and the filament voltage for the final stage has been eliminated, the two most cornrnon causes of voltage distortion in limiters are not present.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A voltage limiter comprising a gas filled electron tube having a cold cathode and an anode, first resistor means connected in series with said cathode, a regulated power supply to supply energy to said gas tube, a second resistor connecting the positive side of said power supply to said anode, a third resistor connecting the positive side of said power supply to the junction between said cathode and said said first resistor means, the negative side of said power supply being connected to the end of said first resistor which is remote from said cathode, means con* nected to said anode for preventing said gas tube from conducting in the absence of an input signal, means for rendering said gas tube conductive in the presence of a positive input signal, and output terminals connected across said first resistor means whereby a first constant output voltage other than zero is applied to said output terminals in the absence of an input signal and second constant output voltage is applied to said output terminals in the presence of a positive input signal.

2. The voltage limiter described in claim l in which said means for preventing said gas tube from conducting comprises a first vacuum tube having a first anode and a first cathode, and a fourth resistor connected in series with said first cathode, said first anode being connected to the junction of said second resistor and said anode of said gas tube whereby the voltage applied to said gas tube anode is reduced when said first vacuum tube conducts.

3. The Voltage limiter described in claim 2 in which said means forrenderiug said gas tube conductive comprises a second vacuum tube having a second anode, a second cathode and a second control grid, and means for injecting an inputsignal into said second control grid, said second cathode being connected to the junction of said first cathode and said fourth resistor whereby conduction through said second vacuum tube initiated by a positive input signal biases said first vacuum tube beyond cut-oli.

4. A voltage limiter comprising a first vacuum tube having a first anode, a first cathode, and a first control grid; a second vacuum tube having a second anode and a second cathode; means for injecting au input signal into said iirst control grid; said iirst cathode being connected to said second cathode; a tirst resistor connecting said first and said second cathodes toground; a gas tube having a third anode and a third cathode; said second anode being connected to said third anode; a regulated power supply having a first terminal and a second terminal; said first terminal being connected to ground; a second resistor connecting said second anode and said third anode to said second power supply terminal; a third resistor connecting said third cathode to ground; a fourth resistor connecting said second power supply terminal to the 4 junction between said third resistor and said third cathode; and output terminals connected to the junction of said third resistor and said third cathode and to ground.

References Cited in the lile of this patent UNITED STATES PATENTS 2,045,542 Koch June 23, 1936 2,486,391 Cunningham Nov. l, 1949 2,490,562 Dorsten Dec. 6, 1949 2,653,237 Johnstone et al. Sept. 22, 1953 FOREIGN PATENTS 127,712 Austria Apr. 11, 1932 

